Calculates the value of input according to a specified modulus,
       using integer values.

1  –  Input

       This function takes two parameters: a signed number and a
       modulus. The two must be separated by a comma and enclosed in
       parentheses.

2  –  Output

       An integer number.

3  –  Example

       DTR> PRINT FN$MODI(13,4);

         FN$MODI

                     1

       DTR> PRINT FN$MODI(-13,4);

         FN$MODI

                   -1

       DTR>